Before an aircraft, automobile or other machinery is repainted, it is generally necessary to remove the old paint. The most efficient way to remove old paint is to blast clean the machinery. Originally, sand was used as the abrasive media in such cleaning operations. However, sand has a drawback in that it typically breaks down during its first use to the extent that it is not generally reusable. Additionally, sand has a relatively high specific gravity and for some blasting operations, such as cleaning aircraft, it can create undesirable stress points in the aircraft frame. Therefore, several artificial abrasive materials have been developed that are reusable. The artificial blasting materials used for cleaning operations are typically fashioned from plastics and are generally somewhat lighter than sand. However, even plastic abrasive materials tend to break down after several uses.
In order to recycle the blasting media, it must be collected and separated from dust and debris that accumulates during blasting. At times it is also necessary to separate heavy particles such as sand, rocks and metal flakes from the blasting media to prevent damage to the machinery being cleaned during blasting operations. This is particularly important when painting aircraft since any metallic flakes, pebbles or the like that are entrained with the media during blasting operations can damage the airframe. Accordingly, there is a need for mechanisms capable of cleaning the recycled blasting materials. In large scale blasting operations such as large aircraft painting facilities, there are extended periods of time during which the blasting materials are used. Accordingly, there is a need for recycling systems capable of operating substantially continuously without requiring extensive maintenance or operator attention.
There are a wide variety of cyclone separators that have been developed to separate the lighter particles such as dust from the recycled blasting media. However, such devices are not particularly well adapted to separating heavier particles from the blasting media or to classify the recycled media by size. Screens can readily be used to classify the blasting materials by size. Specifically, large mesh screens can be used to separate large items, such as masking tape, paper, hardware and the like from the recycled media. Similarly, fine mesh screens can be used to separate the small grained particles (such as broken down blasting media that is unsuitable for reuse) from the good blasting media. However, such screen systems are incapable of classifying the blasting materials by density. Therefore, there is a need for a mechanism capable of continuously cleaning recycled blast media that is capable of classifying the recycled materials by both density and size.